/* This file is part of the Palabos library.
 * Copyright (C) 2009 Jonas Latt
 * E-mail contact: jonas@lbmethod.org
 * The most recent release of Palabos can be downloaded at 
 * <http://www.lbmethod.org/palabos/>
 *
 * The library Palabos is free software: you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * The library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

/** \file
 * Helper functions for the implementation of MRT (multiple relaxation
 * time) dynamics. This file is all about efficiency.
 * The generic template code is specialized for commonly used Lattices,
 * so that a maximum performance can be taken out of each case.
 */
#ifndef D3Q13_TEMPLATES_H
#define D3Q13_TEMPLATES_H

#include "core/globalDefs.h"
#include "latticeBoltzmann/nearestNeighborLattices3D.h"
#include "core/cell.h"
#include "core/util.h"


namespace plb {

/// Helper functions for the (somewhat special) D3Q13 lattice
template<typename T>
struct d3q13Templates {
    typedef descriptors::D3Q13Descriptor<T> Descriptor;

    /// BGK collision step
    static T collision( Cell<T,descriptors::D3Q13Descriptor>& cell,
                        T rho, Array<T,Descriptor::d> const& u,
                        T lambda_nu, T lambda_nu_prime)
    {
        const T lambda_e = descriptors::D3Q13Descriptor<T>::lambda_e;
        const T lambda_h = descriptors::D3Q13Descriptor<T>::lambda_h;

        T uxSqr = u[0]*u[0];
        T uySqr = u[1]*u[1];
        T uzSqr = u[2]*u[2];
        T uSqr = uxSqr + uySqr + uzSqr;

        T s1 = cell[7] + cell[8] + cell[9] + cell[10];
        T s2 = cell[11] + cell[12];
        T s3 = cell[1] + cell[2] + cell[3] + cell[4];
        T s4 = cell[5] + cell[6];
        T sTot = s1 + s2 + s3 + s4;
        T d1 = cell[7] + cell[8] - cell[9] - cell[10];
        T d2 = cell[1] + cell[2] - cell[3] - cell[4];

        T M[13]; // The terms M[0]-M[3] are not used (they correspond
                 // to rho, rho*ux, rho*uy, rho*uz respectively),
                 // but we still use a 13-component vector to preserve
                 // the clarity of the code.
        M[4] = -(T)12*cell[0] + sTot - (T)11/(T)2;
          // The 11/2 correction term in M4 accounts for the fact that
          // cell[i] corresponds to f[i]-ti, and not f[i]
        M[5] = s1 - (T)2*s2 + s3 - (T)2*s4;
        M[6] = d1 + d2;
        M[7] = cell[7] - cell[8] + cell[1] - cell[2];
        M[8] = cell[11] - cell[12] + cell[5] - cell[6];
        M[9] = cell[9] - cell[10] + cell[3] - cell[4];
        M[10] = d1 - d2;
        M[11] = -cell[7] + cell[8] + s2 + cell[1] - cell[2] - s4;
        M[12] = cell[9] - cell[10] - cell[11] + cell[12]
                - cell[3] + cell[4] + cell[5] - cell[6];
        T Mneq[13]; // The terms Mneq[0]-Mneq[3] are not used (they are
                    // actually all zero, because of conservation laws),
                    // but we still use a 13-component vector to preserve
                    // the clarity of the code.
        Mneq[4] = M[4] + (T)11/(T)2*rho - (T)13/(T)2*rho*uSqr;
        Mneq[5] = M[5] - rho*( (T)2*uxSqr-(uySqr+uzSqr) );
        Mneq[6] = M[6] - rho*( uySqr-uzSqr );
        Mneq[7] = M[7] - rho*( u[0]*u[1] );
        Mneq[8] = M[8] - rho*( u[1]*u[2] );
        Mneq[9] = M[9] - rho*( u[0]*u[2] );
        Mneq[10] = M[10];
        Mneq[11] = M[11];
        Mneq[12] = M[12];

        Mneq[4]  *= lambda_e  / (T)156;
        Mneq[5]  *= lambda_nu / (T)24;
        Mneq[6]  *= lambda_nu / (T)8;
        Mneq[7]  *= lambda_nu_prime / (T)4;
        Mneq[8]  *= lambda_nu_prime / (T)4;
        Mneq[9]  *= lambda_nu_prime / (T)4;
        Mneq[10] *= lambda_h / (T)8;
        Mneq[11] *= lambda_h / (T)8;
        Mneq[12] *= lambda_h / (T)8;

        T F1 = Mneq[4] + Mneq[5] + Mneq[6];
        T F2 = Mneq[4] + Mneq[5] - Mneq[6];
        T F3 = Mneq[4] - (T)2*Mneq[5];

        cell[0]  -= (T)-12*Mneq[4];
        cell[1]  -= F1 + Mneq[7]                -Mneq[10]+Mneq[11];
        cell[2]  -= F1 - Mneq[7]                -Mneq[10]-Mneq[11];
        cell[3]  -= F2                  +Mneq[9]+Mneq[10]         -Mneq[12];
        cell[4]  -= F2                  -Mneq[9]+Mneq[10]         +Mneq[12];
        cell[5]  -= F3          +Mneq[8]                 -Mneq[11]+Mneq[12];
        cell[6]  -= F3          -Mneq[8]                 -Mneq[11]-Mneq[12];
        cell[7]  -= F1 + Mneq[7]                +Mneq[10]-Mneq[11];
        cell[8]  -= F1 - Mneq[7]                +Mneq[10]+Mneq[11];
        cell[9]  -= F2                  +Mneq[9]-Mneq[10]         +Mneq[12];
        cell[10] -= F2                  -Mneq[9]-Mneq[10]         -Mneq[12];
        cell[11] -= F3          +Mneq[8]                 +Mneq[11]-Mneq[12];
        cell[12] -= F3          -Mneq[8]                 +Mneq[11]+Mneq[12];

        return uSqr;
    }

    /// BGK collision step with density correction
    static T constRhoCollision( Cell<T,descriptors::D3Q13Descriptor>& cell,
                                T rho, Array<T,Descriptor::d> const& u,
                                T ratioRho,
                                T lambda_nu, T lambda_nu_prime)
    {
        const T uSqr = VectorTemplate<T,descriptors::D3Q13Descriptor>::normSqr(u);
        return uSqr;
    }
}; // struct d3q13Templates

}  // namespace plb

#endif
